1. Field of the Invention
The invention is directed to a registration method for navigation-guided medical interventions of the type wherein a coordinate transformation that is employed for navigation is determined between a coordinate system of a position acquisition system and a measurement volume of an X-ray device. The invention is also directed to an apparatus for the implementation of the method. The method and apparatus of the invention do not require patient-associated markers.
2. Description of the Prior Art
Navigation is increasingly being used for supporting medical interventions at living subjects, this being understood as the guidance of a medical instrument relative to a subject or relative to a tissue region of subject being treated, that is supported by means of optical image information. An image of the instrument is mixed into a 2D or 3D image of the subject acquired with the X-ray device. In this way, an operator can guide an instrument that has at least partially penetrated into the subject so that its tip is no longer directly visible, for example due to the penetration into body tissue, relative to the tissue region of the subject on the basis of the image information without a risk of unintentionally harming the subject.
In order to enable such a navigation-guided intervention, i.e. in order to be able to mix an image of the instrument into image information of a subject in a manner that is accurate as to position and orientation, it is necessary to produce a mathematical relationship in the form of a coordinate transformation between a coordinate system of the image information of the subject or a coordinate system of the reconstructed volume of the subject and a coordinate system with respect which the positions of the instrument are indicated. To this end, artificial markers are sometimes arranged at the subject or anatomical markers, for example distinct bone structures, are defined. The anatomical or artificial markers (patient-associated markers) must be clearly visible in the image information of the subject registered with the X-ray device and must be easily accessible at the subject. For example, the artificial markers are secured to the skin surface of the subject order to be able to undertake a registration, which is understood to mean the determination of the spatial transformation rule between the coordinate system wherein the positions of the instrument to be navigated are defined and the coordinate system of the image information or of the reconstructed volume of the subject. The markers usually must be individually approached with the instrument in a specified sequence in order to be able to determine the coordinate transformation between the two coordinate systems. In extremely precise medical interventions, the markers are secured to the body of the subject so as to be immobile. The attachment of a stereotactic frame to the head of a patient and the attachment of markers in bones or at the spinal column of a patient are as examples. The attachment of the markers partly ensues in a separate operation since the markers must already be applied before a pre-operative imaging that is frequently employed for navigation.
The attachment and registration of the markers, accordingly, is a relatively unpleasant procedure for a patient and is also relatively time-consuming for an operator in preparing a navigation-guided intervention.